The bone maturation and physical growth of prematurely born Macaca mulatta are studied from birth to 24 months of age. A group of 12 prematurely born (range 140-150 days of gestation) monkeys of both sexes are observed. The growth parameters such as bone maturation (skeletal age), body weight, "dental age," cranial dimension, sitting height, length of upper and lower extremities are measured and compared with the data obtained from full-term animals. A correlation between appendicular bone maturation and gestational age is being established.